/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.streaming.runtime.operators.util;

import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.eventtime.TimestampAssigner;
import org.apache.flink.api.common.eventtime.TimestampAssignerSupplier;
import org.apache.flink.api.common.eventtime.Watermark;
import org.apache.flink.api.common.eventtime.WatermarkGenerator;
import org.apache.flink.api.common.eventtime.WatermarkGeneratorSupplier;
import org.apache.flink.api.common.eventtime.WatermarkOutput;
import org.apache.flink.api.common.eventtime.WatermarkStrategy;
import org.apache.flink.streaming.api.functions.AssignerWithPeriodicWatermarks;

import static org.apache.flink.util.Preconditions.checkNotNull;

/**
 * An adapter that wraps a {@link AssignerWithPeriodicWatermarks} into a {@link WatermarkGenerator}.
 */
@Internal
@SuppressWarnings("deprecation")
public final class AssignerWithPeriodicWatermarksAdapter<T> implements WatermarkGenerator<T> {

    private final AssignerWithPeriodicWatermarks<T> wms;

    public AssignerWithPeriodicWatermarksAdapter(AssignerWithPeriodicWatermarks<T> wms) {
        this.wms = checkNotNull(wms);
    }

    @Override
    public void onEvent(T event, long eventTimestamp, WatermarkOutput output) {}

    @Override
    public void onPeriodicEmit(WatermarkOutput output) {
        final org.apache.flink.streaming.api.watermark.Watermark next = wms.getCurrentWatermark();
        if (next != null) {
            output.emitWatermark(new Watermark(next.getTimestamp()));
        }
    }

    // ------------------------------------------------------------------------

    /**
     * A WatermarkStrategy that returns an {@link AssignerWithPeriodicWatermarks} wrapped as a
     * {@link WatermarkGenerator}.
     */
    public static final class Strategy<T> implements WatermarkStrategy<T> {
        private static final long serialVersionUID = 1L;

        private final AssignerWithPeriodicWatermarks<T> wms;

        public Strategy(AssignerWithPeriodicWatermarks<T> wms) {
            this.wms = checkNotNull(wms);
        }

        @Override
        public TimestampAssigner<T> createTimestampAssigner(
                TimestampAssignerSupplier.Context context) {
            return wms;
        }

        @Override
        public WatermarkGenerator<T> createWatermarkGenerator(
                WatermarkGeneratorSupplier.Context context) {
            return new AssignerWithPeriodicWatermarksAdapter<>(wms);
        }
    }
}
